The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Resistive heaters are used in a variety of applications to provide heat to a target and/or environment. One type of resistive heater known in the art is a cartridge heater, which generally consists of a resistive wire heating element wound around a ceramic core. A typical ceramic core defines two longitudinal bores with power/terminal pins disposed therein. A first end of the resistive wire is electrically connected to one power pin and the other end of the resistive wire electrically connected to the other power pin. This assembly is then inserted into a tubular metal sheath of a larger diameter having an open end and a closed end, or two open ends, thus creating an annular space between the sheath and the resistive wire/core assembly. An insulative material, such as magnesium oxide (MgO) or the like, is poured into the open end of the sheath to fill the annular space between the resistive wire and the inner surface of the sheath.
The open end of the sheath is sealed, for example by using a potting compound and/or discrete sealing members. The entire assembly is then compacted or compressed, as by swaging or by other suitable process, to reduce the diameter of the sheath and to thus compact and compress the MgO and to at least partially crush the ceramic core so as to collapse the core about the pins to ensure good electrical contact and thermal transfer. The compacted MgO provides a relatively good heat transfer path between the heating element and the sheath and it also electrically insulates the sheath from the heating element.
In order to determine the proper temperature at which the heaters should be operating, discrete temperature sensors, for example thermocouples, are placed on or near the heater. Adding discrete temperature sensors to the heater and its environment can be costly and add complexity to the overall heating system.